Short-term sympathoadrenal inhibition augments the thermogenic response to β-adrenergic receptor stimulation

Sedentary behavior is associated with an attenuated thermogenic response to β-adrenergic receptor (β-AR) stimulation, an important regulator of energy expenditure (EE) in humans. Chronic stimulation of β-ARs, via heightened activity of the sympathoadrenal system, leads to diminished β-AR function. We have investigated the hypothesis that the thermogenic response of sedentary adults to β-AR stimulation will be increased during short-term sympathoadrenal inhibition. Using a randomly ordered, repeated measures study design, resting EE (REE; indirect calorimetry, ventilated hood technique) and the % increase in EE above REE (%ΔEE) during acute i.v. isoproterenol administration (nonselective β-AR agonist; 6, 12, and 24 ng/kg fat-free mass per min) were determined in 16 sedentary adults (nine females and seven males, 25±1 years, body mass index: 26.1±0.9 kg/m2, maximal oxygen uptake: 40±2 ml/kg per min (mean±s.e.m.)) in the basal state and on the 6th day of transdermal clonidine administration (centrally acting α2-AR agonist; 0.2 mg/day). Relative to baseline, clonidine inhibited sympathoadrenal activity, as evidenced by decreased plasma norepinephrine concentration (1.04±0.13 vs 0.34±0.03 nmol/l; P